Means currently for measuring hydrostatic pressure for liquid level applications generally comprise a differential pressure device mounted at the surface of the body of liquid to be measured wherein one portion of the sensing element is vented to the immediate atmosphere and wherein a pressure equivalent to the hydrostatic head is applied to the opposite side of the sensing device to establish the differential. When the aforementioned device is used to monitor the level of a deep well, for example, an air pressure line must be introduced below the lowest level of the well to be sensed. An air pressure source must be relied upon to displace the water from the sensing pipe.
Another sensing device employs an hermetically sealed transducer wherein one reference is provided by a vacuum and the pressure is directly sensed below the surface of the liquid involved. Because of the vacuum containment, the housing must be specially constructed in order to avoid any leaks or damage to the pressure-sensing means within the housing. When the vacuum-sealed units are used in liquids of varying depths, the pressure differential readings will be altered by changes in atmospheric conditions above the level of the surface of the liquid being measured.
The purpose of this invention is to provide a liquid level sensor for complete submersion below the level of the liquid being sensed without relying upon a vacuum-sealed device or relying upon an auxiliary source of compressed air or gas. The sensor of the instant invention does not require auxiliary means for compensating for changes in the atmospheric pressure above the surface of the liquid.